Xylylene dicarbamates and process for preparing the same

ABSTRACT

Novel xylylene dicarbamate and nucleus-substituted derivatives thereof expressed by the following formula WHEREIN R stand for an alkyl group of one to four CARBON ATOMS AND N IS O or an integer of 1 to 4, AND A PROCESS FOR THE PREPARATION OF SAID XYLYLENE DICARBAMATES.

United States Patent 1 Huang et al.

[54] XYLYLENE DICARBAMATES AND PROCESS FOR PREPARING THE SAME [75]Inventors: Ching Yun Huang; Tomotaka Qnj zpka, both of Osaka; TamotsuMaeno, Yokohama; Teruyuki; Ninomiya, Osaka, all of J apan [52] U.S. Cl...260/482 B, 117/140 A, 117/155 L,

260/78 R, 260/482 C [51] Int. Cl ..C07c 125/04 [58] Field of Search..260/482 C, 482 B [56] References Cited UNITED STATES PATENTS 2,934,5594/1960 Beinfort et al. ....260/482 B 51 Feb. 20, 1973 FOREIGN PATENTS ORAPPLlCATlONS 839,408 6/1960 Great Britain ..260/482 PrimaryExaminer-Lorraine A. Weinberger Assistant Examiner-Paul J. KillosAttorney-Sherman and Shalloway [5 7 ABSTRACT Novel xylylene dicarbamateand nucleus-substituted derivatives thereof expressed by the followingformula wherein R stand for an alkyl group of one to four carbon atomsand n is O or an integer of l to 4, and a process for the preparation ofsaid xylylene dicarbamates.

11 Claims, No Drawings XYLYLENE DICARBAMATES AND PROCESS FOR PREPARINGTHE SAME This invention relates to xylylene dicarbamates and a processfor the preparation of the same. More specifically, it relates to novelxylylene dicarbamate and nucleus-substituted derivatives thereofexpressed by the following formula 01120 c ONH: I cn-zocoNn-i wherein Rstands for an alkyl group of one to four carbon atoms and n is or aninteger of l to 4, and a process for the preparation of said dicarbamatederivatives.

As processes for preparing esters of carbamic acid the following havebeen known (I) a process comprising a reaction of an alcohol with urea,(2) a process comprising subjecting an alcohol to an ester-exchangereaction with a lower alkyl ester of carbamic acid and (3) a processcomprising a reaction of an alcohol with phosgene to form an ester ofchloroformic acid and a reaction of the ester with ammonia. Esters ofdicarbamic acid can be optionally prepared from glycols in accordancewith the above-mentioned processes. Further, a process has been knownfor the preparation of benzyl carbamates having an aromatic nucleus inthe molecule by a reaction of a benzyl alcohol with urea.

However, no process has been known for the preparation of xylylenedicarbamates from xylylene glycols. Unlike aliphatic glycols, xylyleneglycols have a tendency to cause self-condensation quite easily evenunder a weakly acidic condition and further, at elevated temperaturestend to turn into polyethers. Such properties are prominent particularlyin xylylene glycols which have an alkyl substituent in the aromaticnucleus.

Still further, xylylene glycols have an extremely high boiling point ascompared with aliphatic glycols. Because of such high boiling point andthe above-mentioned tendency toward self-condensation at elevatedtemperatures, xylylene glycols cannot be distilled by conventional meansadopted in laboratories or industries.

In the conventional process for the preparation of alkyl carbamates, analcohol is generally used in excess based on urea, and the excessivealcohol can be recovered by distillation after completion of thereaction. As the grate of the reaction between an alcohol and urea islow, the operation above-mentioned is usually conducted in the presenceof an excess of one of the reactants in order to accelerate the reactionand prevent urea from being converted into cyanuric acid as aby-product. However, in the case of xylylene glycols it is impossiblebecause of the above-mentioned properties of xylylene glycols to usethem in excess based on the urea and distill unchanged glycols aftercompletion of the reaction. It is known that in the process forpreparing benzyl carbamate from benzyl alcohol and urea, the reaction isconducted at a high temperature such as 170-l80C in the presence of anacidic catalyst such as sulfuric acid, phosphoric acid and aluminumchloride [Kogyo Kagaku Zasshi, vol. 66, page 514 (1963)]. In view of thecharacteristic proper- CHZOCONIiZ R j, I cugocomn wherein R stands foran alkyl group of one to four carbon atoms and n is 0 or an integer of lto 4, which comprises reacting a xylylene glycol expressed by theformula wherein R and n are as defined above, with urea at a temperatureof to C.

In accordance with this invention, a process is further provided for thepreparation of xylylene dicarbamates expressed by the formula R\CH-iOCONH: j CH-zOCONH2 wherein R stands for an alkyl group of one tofour carbon atoms and n is 0 or an integer of l to 4, which comprisesreacting a xylylene glycol expressed by the formula onion 7,, ltxlmonwherein R and n as def ned above,

with an ester of carbamic acid expressed by the formula H NCOOR' whereinR stands for an alkyl group of one to four carbon atoms, at atemperature of 120 to 18C.

The xylylene glycol to be used as one of the starting materials in thisinvention is expressed by the following general formula wherein R standsfor an alkyl group of one to four carbon atoms and n is 0 or an integerof l to 4, and when the group (R contains a plurality of Rs, they may bethe same or different. Specific examples of such xylylene glycol areo-xylylene glycol, m-xylylene glycol, p-xylylene glycol and xylyleneglycols which have an alkyl substituent in the aromatic nucleus, such as4-methyl-m-xylylene glycol,

3 4-ethyl-m-xylylene glycol, 4-isopropyl-m-xylylene glycol,4-tert.-butylm-xylylene glycol, 4,5-dimethyl-oxylylene glycol,4,6-dimethyl-m-xylylene glycol, 2,5- dimethyl-p-xylylene glycol,2,4,6-trimethyl-m-xylylene glycol, 2,4,5-trimethyl-m-xylylene glycol and2,3,5,6-

' tetramethyl-p-xylylene glycol.

In the first process of this invention wherein urea is used as the otherstarting material, it is sufficient to use urea in a stoichiometricamount based on the abovementioned xylylene glycol, namely in an amountof about 2 moles per mole of the xylylene glycol. Of course, it ispossible to use urea in an amount greater than the stoichiometricamount. In case urea is used in an excessive amount based on thexylylene glycol, the unchanged urea can be easily separated from thereaction product by the method of separation and purification which maybe detailed hereinbelow. Accordingly, the use of an excessive amount ofurea does not cause any disadvantages. In this invention it is generallydesired to use urea in an amount of 2 to 3 moles per mole of thexylylene glycol.

In conducting the first process of this invention special attention mustbe paid to the reaction temperature and the separation and purificationof the reaction product in order that the reaction between the xylyleneglycol and urea may be advanced smoothly and that a xylylene dicarbamatemay be obtained in high purity. More specifically, the temperature rangeis very critical in the reaction of the xylylene glycol with urea, andthe reaction must be effected at 135 to 160C, preferably 140 to 155C. Ata temperature lower than l35C, the reaction rate is too low and theintended xylylene dicarbamate is hardly formed, though a xylylene glycolmonocarbamate can be obtained. On the other hand, at a temperaturehigher than 160C, a resinous product is readily formed and itsseparation from the intended product is difficult, with the result thatthe yield of intended product is lowered. In short, the reaction isallowed to progress conveniently at a temperature within the limitedrange of 135 to 160C.

At a temperature of the above-mentioned range the reaction is allowed toadvance sufficiently even in the absence of a catalyst. It is possibleto use a catalyst so as to perform the reaction more efficiently. As thecatalyst, catalysts ordinarily used for the reaction of preparingcarbamates from alcohols and urea may be used, except those which are.acidic. The use of an acidic catalyst such as sulfuric acid andphosphoric acid is not suitable for attaining the object of thisinvention, because such acidic catalyst causes polycondensation of thexylylene glycol. Catalysts to be used particularly preferably for theobject of this invention include carboxylic acid salts of metals such aszinc and lead, e.g., acetates of such metals; stannic and stannouschlorides; and organotin compounds.

As the organotin compound, tin compounds expressed by the followingformulae A SnX and A SnY wherein A stands for an alkyl or alkoxy group,X is a halogen atom, a thioalkoxy or hydroxyl group, or a carboxylicacid residue, Y stands for an oxygen or sulfur atom and m is 1, 2 or 3are generally used.

Specific examples of the organotin compound are trin-butyl tin acetate,di-n-butyl tin diacetate, di-n-butyl tin dilaurate, di-n-butyl tindilauryl mercaptide, dimethyl tin dichloride, di-n-butyl tin dichloride,di-nbutyl tin sulfide, bis(2-ethylhexyl) tin oxide, Z-ethylhexyl stannicacid and trimethyl tin hydroxide.

These catalysts are used in amount generally employed for preparation ofcarbamates, e.g., 0.5 to 10 percent by weight, preferably 1 to 6 percentby weight, based on the xylylene glycol.

The reaction may be effected in the absence of a solvent, that is, inthe molten state of urea and the xylylene glycol. It is also possible toconduct the reaction in an inert organic solvent such astrichlorobenzene.

The reaction is allowed to advance sufficiently under atmosphericpressure, but it may be preferable that the reaction is carried outunder somewhat reduced pressure since ammonia is liberated from thereaction medium, and furthermore, no particular disadvantage is causedin the reaction under somewhat elevated pressure. The reaction time of10 hours or more is sufficient.

The reaction mixture obtained by the reaction conducted under theabove-mentioned conditions contains a xylylene glycol monocarbamate, theunchanged xylylene glycol and urea, a small amount of a resinousbyproduct and the catalyst optionally used in addition to the intendedxylylene dicarbamate.

Although the intended xylylene dicarbamate may be separated from suchreaction mixture by conventional techniques other than distillation,e.g., by recrystallization, extraction or the like, it is impossible toobtain the intended product of a high purity by such conventionaltechniques.

It has now been found that when the reaction mixture obtained in theabove-mentioned first process is treated with an aromatic hydrocarbonhaving 'six to nine (inclusive) carbon atoms, the unchanged xylyleneglycol, the xylylene glycol monocarbamate, the catalyst residue and thelike are dissolved in the aromatic hydrocarbon and that when thereaction mixture undissolved in aromatic hydrocarbon is further treatedwith nitrobenzen, the substances other than urea are dissolved innitrobenzene and the intended xylylene dicarbamate can be recovered inhigh purity from the nitrobenzene solution.

Thus, in accordance with this invention, a process for recovering axylylene dicarbamate of a high purity from the above-mentioned reactionmixture is also provided. This purification process will now be detailedby referring to a crude reaction mixture obtained by employing anorganotin compound as the catalyst. First the crude reaction mixture istreated with a hot aromatic hydrocarbon having 6 to nine carbon atoms.The intended xylylene dicarbamate, the unchanged urea and a resinousby-product are insoluble in the hot aromatic hydrocarbon, while thexylene glycol monocarbamate, by-product the unchanged xylylene glycoland the organotin compound used as the catalyst are soluble in the hotaromatic hydrocarbon. Thus, they are separated easily by filtration. Asthe aromatic hydrocarbon having six to nine carbon atoms to be used forthis purpose, benzene, toluene, xylene, ethyl benzene, cumene,pseudocumene, mesitylene and the like may be cited. in the treatment ofthe reaction mixture with the above-mentioned aromatic hydrocarbon, itis essential that the treatment temperature should not be lower than 70C. When the aromatic hydrocarbon is distilled off from the filtrate, amixture remains comprising the xylylene glycol monocarbamate which is anintermediate of the intended xylylene dicarbamate, the unchangedstarting xylylene glycol and the catalyst. This mixture may be recycledto the reaction and use as a part of the starting materials.

The filtration residue comprising the intended xylylene dicarbamate, theunchanged urea and a resinous by-product is treated with nitrobenzene.Since urea is insoluble in nitrobenzene even at elevated temperatures,the unchanged urea can be separated from the filtration residue byadding thereto nitrobenzene, heating the mixture and subjecting it tofiltration. It is preferable that this treatment of nitrobenzene iseffected at a temperature of 100 to 140C. When the nitrobenzene solutionobtained after separation of urea is allowed to cool, the xylylenedicarbamate is precipitated as crystals. The xylylene dicarbamate ishardly soluble in nitrobenzene at low-temperatures, while the resinousproduct is easily soluble in nitrobenzene even at those temperatures.Accordingly, the intended product precipitated as crystals can be easilyrecovered by filtration. The formation of crystals of the intendedproduct may be efficiently accomplished only by cooling the nitrobenzenesolution to room temperature, and it is unnecessary to lower thetemperature below room temperature by ice cooling or the like.Nitrobenzene can be easily recovered by distillation from the filtrateobtained after separation of the intended xylylene dicarbam ate.

In the above-mentioned process of separation and purification, if thecatalyst used in the reaction is insoluble in the hot aromatichydrocarbon, it may be separated in the treatment with nitrobenzene, andfurthermore if the catalyst is soluble in nitrobenzene, it may beseparated when the precipitated product by cooling is filtered from thenitrobenzene solution. The product separated by the above-mentionedprocess has a sufficiently high purity, but if necessary, it may befurther purified by means of purification methods described below.

In accordance with the second process of this invention, a xylyleneglycol expressed by the above-mentioned formula (II) is allowed to reactwith a lower alkyl ester of carbamic acid expressed by theabovementioned formula (III) at a temperature of 120 to 180C.

As the lower alkyl ester of carbamic acid, alkyl esters of the formulaNI-I COOR' (in which R is an alkyl group of one to four, carbon atoms),such as methyl carbamate, ethyl carbamate, n-propyl carbamate, isopropylcarbamate, n-butyl carbamate and isobutyl carbamate may be named. It issufficient to use the lower alkyl ester of cabamic acid in an amount of2 moles per mole of the xylylene glycol, but it is permissible to usethe ester in an excessive amount. However, the use of the ester in anextremely excessive amount is not preferred because in such case it isnecessary to increase the amount of the solvent. Accordingly, it isdesired to use the ester in an amount of at most 3 moles per mole of thexylylene glycol.

In conducting the second process of this invention special attentionsmust be paid to reaction conditions, particularly the reactiontemperature. More specifically, the reaction of the xylylene glycol witha lower alkyl ester of carbamic acid is effected at a temperature of to180C, preferably to C, since at a temperature lower than 120C, the rateof the reaction is extremely low regardless of the class and amount ofthe catalyst, and only a xylylene glycol monocarbamate is obtained asthe reaction product, and on the other hand, at a temperature higherthan C, formation of a resinous byproduct is extreme and the yield ofthe intended xylylene dicarbamate is lowered. Accordingly, in conductingthe second process of this invention it is also possible to carry outthe reaction at two stages where a xylylene glycol monocarbamate ispreliminarily formed at a temperature lower than 120C, and then it isheated to a temperature of 120 to 180C to form the intended xylylenedicarbamate.

In accordance with the above-mentioned second process of this invention,the intended xylylene dicarbamate can be formed even without use of acatalyst only by carrying out the reaction at temperatures within theabove-mentioned range. It is, however, generally preferable to use acatalyst for the purpose of accelerating the reaction. The reaction ofthe second process of this invention is an ester-exchange reaction.Accordingly, among conventional cstcr-cxchangc catalysts are chosenthose which are not acidic. As such catalyst, aluminum alkoxides andtetralkyl titanates may be cited, the latter being especially preferred.Further, it has been found that since these catalysts are soluble invarious solvents which will be described below, when they are used incombination with these solvents, the intended xylylene dicarbamate canbe isolated without containing the catalyst only by subjecting thereaction mixture to filtration. Compounds of other metals known as thecatalysts for the ester-exchange reaction are soluble partially or notat all in these solvents. Accordingly, one of features of this inventionresides in the discovery that such characteristic property of thesecatalysts can be utilized conveniently.

Preferable examples of the tetralkyl titanate to be used in thisinvention are tetra-iso-propyl titanate, tetrabutyl titanate,tetra-2-ethylhexyl titanate and tetrastearyl titanate. As the aluminumalkoxide, aluminum ethoxide and aluminum iso-propoxide may be cited. Theamount of the catalyst to be used is 0.1 to 5 percent by weight,preferably 0.5 to 3 percent by weight, based on the xylylene glycol.

In the second process of this invention it is preferable to use asolvent. Since a lower alkyl ester of carbamic acid, one of the startingmaterials, is molten at a reaction temperature within theabove-mentioned range and acts as a suitable solvent, the second processof this invention can be carried out even without using any solvent.However, since the intended xylylene dicarbamate is precipitated as acrystal in the reaction medium, it is preferable to use a solvent,whereby the uniform dispersion of the reactants and catalyst can beattained, the partial heating can be prevented and the separation of theintended product can be accomplished conveniently. It is desired thatsolvents used in the second process of this invention have no activehydrogen atom in the molecule, have a boiling point under atmosphericpressure of more than 1 15C so that the reaction temperature may bemaintained above 120C and are able to dissolve xylylene glycols andlower alkyl esters of carbamic acid at least at reaction temperaturesmentioned above. As the solvent meeting the above requirements, aromatichydrocarbons having a boiling point higher than 115C, such as ethylbenzene, mixed xylene, mand p-xylenes, mesitylene, pseudocumene,iso-propyl benzene and pcymene; chlorobenzene derivatives such asmonochlorobenzene, o-, mand p-dichlorobenzenes, and 1,2,3- and1,2,4-trichlorobenzenes; and alkoxy benzene derivatibes such as anisoland phenetole may be named. It is sufficient in principle to use thesolvent in an amount such that the starting mixture may be kepthomogeneous at initiation of the reaction and the unchanged reactants,intermediate and catalyst may be dissolved therein at elevatedtemperatures at completion of the reaction. Generally, the solvent isused in an amount of 0.3 to 1.0 liter per mole of the starting xylyleneglycol.

It has been found that these solvents can dissolve not only theunchanged starting materials but also an intermediate product, namely, axylylene glycol monocarbamate at elevated temperatures and that they canfurther dissolve the above-mentioned catalysts. Accordingly, if thereaction is effected with the use of such solvents and the filtration iscarried out at elevated temperature after completion of the reaction, itis possible to recover only the intended xylylene dicarbamate. Sinceboth the unchanged xylylene glycol and the intermediate xylylene glycolmonocarbamate have an extremely high boiling point, it is almostimpossible to remove these impurities by distillation, whereby theintended product in the reaction mixture is likely to undergo thermaldecomposition. The filtrate obtained from separation of the intendedproduct which contains the unchanged starting materials, theintermediate product and the catalyst, can be recycled to the reactionas it is. Accordingly, the starting materials and catalyst can beutilized efficiently.

Accordingly, the process of this invention in which xylylenedicarbamates of a high purity can be recovered by a simple filtrationtechnique with the use of the above-mentioned solvents is a processwhich can be worked industrially conveniently.

As described above, xylylene dicarbamates prepared according to thisinvention are of a high purity, and they are usually used for variouspurposes as they are recovered. if further purification is required, itis possible to adopt the following methods as embodiments ofpurification. Namely, one of the embodiments of purification in thisinvention is a fractional precipitation method which comprises using acombination of a good solvent and a poor solvent for the xylylenedicarbamates. The former is a polar organic solvent, such as methanol,ethanol, dioxane, tetrahydrofuran, acetone, dimethyl formamide andN-methyl-2-pyrolidone, wherein the xylylene dicarbamates areeasily'soluble and the latter is water or an aromatic hydrocarbonwherein the xylylene dicarbamates are almost insoluble, and they must bemiscible with each other. in this method, the purification can beaccomplished by dissolving the crude xylylene dicarbamates in its goodsolvent mentioned above and then adding the poor solvent to the solutionto thereby precipitate the intended product fractionally. The otherembodiment of purification in this invention is a recrystalizationmethod wherein a polar organic solvent such as n-butanol andnitrobenzene may be used.

Thus, in accordance with this invention, novel xy lylene dicarbamatesexpressed by the above-mentioned general formula (I) are provided. Thesenovel xylylene dicarbamates have a structural characteristic that theycontain an aromatic nucleus in the molecule and have two carbamategroups bonded to the aromatic nucleus. Accordingly, various highmolecular weight polymers can be synthesized from novel xylylenecarbamates of this invention by utilizing thestability inherent to thearomatic nucleus and the two functional carbamate groups inthe molecule.More specifically, they can be used as chain-extenders in thepreparation of polyurethanes and as hardening agents for epoxy resins.

Further, the methylol compounds derived from the reaction of thexylylene dicarbamates with formaldehyde may be used as raw materials foradhesives,

laminates, molding materials or fiberand paper-treat-- This inventionwill now be described by referring to examples, but this invention isnot limited by these examples.

EXAMPLEI A reaction vessel equipped with a stirrer, a thermometer, afractionation column and a cooler was charged'with 4,160 g (25 moles) of4,6-dimethyl-m-xylylene glycol, 5350 g (60 moles) of ethyl carbamate and18 liters of mixed xylylenes, which were heated above 100C to. remove asmuch water as possible.

Then, g of tetrabutyl titanate were added and the reaction was effectedat. l30-l40C. Ethanol formed with the advance of the reaction wasdischarged from the top of the column. Since the resulting4,6-dimethylm-xylylene dicarbamate is insoluble in mixed xylylenes, itwas precipitated with the advance of the reaction. When the reaction wasconducted for 3.5 hours at the above-mentioned temperature, about 2,850cc of ethanol were removed. At this point the reaction was stopped. Thereaction mixture was subjected to filtration while the temperature wasabove C. In this way 5,930 g of 4,6-dimethyl-m-xylylene dicarbamate wereobtained in a yield of 94.2 percent based on the starting xylyleneglycol.

The so obtained product was in the form of white, cotton-like crystalsmelting at 198C. The nitrogen analysis value was found to be 1 1.0percent (calculated value l l .1 percent).

After the so obtained dicarbamate was recrystallized from n-butanol, themelting point of the recrystallized product was measured as 198C.

The filtrate obtained at the above filtration step contained smallamounts of unchanged 4,6-dimethyl-m-xylylene glycol and intermediate4,6-dimethyl-m-xylylene glycol monocarbamate, and it could be recycledand used in the next reaction.

EXAMPLE 2 The same reaction vessel as used in Example 1 was charged with4,160 g (25 moles) of 4,6-dimethyl-m-xylylene glycol, 5,350 g (60 moles)of ethyl carbamate and, 18 liters of o-xylene and 150 g of aluminumisopropoxide. The reaction was effected at 140150C. Ethanol formed withthe progress of the reaction was discharged from the reaction system inthe same manner as in Example 1. The reaction was continued for about 7hours, and the reaction mixture underwent filtration while thetemperature of the system was high. In this way 5,780 g of4,6-dimethyl-m-xylylene dicarbamate was obtained in a yield of 91.8percent based on the starting xylylene glycol. The melting point of theproduct was 198C and the nitrogen analysis value was found to be 1 1.0percent.

EXAMPLE 3 In the same reaction vessel as used in Example 1, 4,160 g (25moles) of 2,5-dimethyl-p-xylylene glycol, 5,350 g (60 moles) of ethylcarbamate, 18 liters of mxylylene and 100 g of tetra-iso-propyl titanatewere allowed to react at l35-140C for 4 hours in the same manner as inExample 1. 2,5-Dimethyl-p-xylylene dicarbamate precipitated during thereaction was separated by filtration while the temperature of thereaction mixture was high. Some 5,800 g of pure 2,5- dimethyl-p-xylylenedicarbamate were obtained in the form of white, cotton-like crystalsmelting at 219C. The yield was 92.2 percent based on the startingxylylene glycol and the nitrogen analysis value was found to be 11.1percent (calculated value =11.1 percent).

EXAMPLE 4 The same reaction vessel as used in Example 1 was charged with4,160 g (25 moles) of 4,5-dimethyl-o-xylylene glycol, 4,500 g (60 moles)of methyl carbamate, 15 liters of ethyl benzene and 100 g oftetra-Z-ethylhexyl titanate, and the reaction was conducted at 130-140 Cfor 3.5 hours in the same manner as in Example 1. When the filtration ofthe reaction mixture was effected in the same manner as in Example 1,5,550 g of pure 4,5-dimethyl-o-xylylene dicarbamate in the form ofwhite, cotton-like crystals melting at 206C were obtained in a yield of88.2 percent based on the starting xylylene glycol. The nitrogenanalysis value was found to be 10.9 percent (calculated value 1 1.1percent).

EXAMPLE 5 The same reaction vessel as used in Example 1 was charged with3,450 g (25 moles) of m-xylylene glycol, 4,500 g (60 moles) of methylcarbamate, liters of monochlorobenzene and 100 g of tetrabutyl titanate,and the reaction was carried out at 125130C for 4,5 hours. Aftercompletion of the reaction the temperature of the reaction mixture waslowered at 80C and at this temperature the filtration was effected toyield 5,140 g of white, powdery m-xylylene dicarbamate in a yield of90.3 percent based on the starting xylylene glycol. The melting point ofthe product was 148C and the nitrogen analysis value was found to be12.4 percent (calculated value 12.5 percent).

EXAMPLE 6 A reactor equipped with a stirrer, a thermometer, a cooler anda nitrogen-introducing tube was charged with 83.1 g (0.5 mole) of2,5-dimethyl-p-xylylene glycol and 60 g (1.0 mole) of urea, which wereallowed to react at l40-l45C for 12 hours while passing nitrogen throughthe reactor. After completion of the reaction 150 ml of hot xylene wereadded to the reaction mixture, and the mixture was stirred sufficiently.Then, the precipitate was filtered off at elevated temperatures. Thefiltered residue was admixed with 200 ml of nitrobenzene and dissolvedtherein by heating at about C. Then, the filtration was effected and thefiltrate was allowed to cool to room temperature. The precipitatedproduct was separated by filtration, washed with xylylene and dried. Theobtained product having a melting point of 214C was dissolved in 500 mlof hot dioxane and then water was added to the solution until noprecipitation was observed in the mixed solution. The precipitatedproduct was filtered out and dried. The resulting product had a meltingpoint of 219C, and the nitrogen analysis value was found be 11.3 percent(calculated value 11.1 percent). Thus, it was confirmed that the productwas 2,5-dimethyl-pxylylene dicarbamate. The amount obtained of theproduct was 72.5 g which corresponded to 48 percent of the theoreticalyield.

EXAMPLE 7 A 2-liter capacity reactor equipped with a stirrer, athermometer, a cooler and a nitrogen-introducing tube was charged with831 g (5 moles) of 4,6-dimethyl-mxylylene glycol, 781 g (13 moles) ofurea and 30 g of din-butyl tin laurate, and the reaction was carried outat 145150C for 12 hours while feeding nitrogen gas into the reactor.Ammonia formed with the advance of the reaction was withdrawn from thetop of the cooler. At the initial stage of the reaction the reactantmixture was in the uniform molten state, but with the advance of thereaction, 4,6-dimethyl-m-xylylene dicarbamate was precipitated in thereaction system. After completion of the reaction, 1 liter of hottoluene was added to the reaction mixture, and the unchanged startingxylylene glycol, intermediate xylylene glycol monocarbamate and thecatalyst were dissolved therein, followed by filtration. The soseparated product was admixed with 6 liters of nitrobenzene at about C,followed by filtration. When the filtrate was cooled to roomtemperature, 4,6 -dimethyl-m-xylylene dicarbamate was precipitated,which was then recovered by filtration, washed with toluene and dried.Some 880 g of 4,6- dimethyl-m-xylylene dicarbamate were obtained in ayield of 70 percent. The melting point of the product was 197-198C andthe nitrogen analysis value was found to be 1 1.2 percent (calculatedvalue 11.1 per- 'cent).

EXAMPLE 8 The same reactor as used in Example 7 was charged with 249 g(1.5 moles) of 4,6-dimethyl-m-xylylene glycol, 234 g (3.9 moles) ofurea, 10 g of di-n-butyl tin dilaurylmercaptide and 1.2 liters of 1,2,4-trichlorobenzene, and the reaction was effected at l45150C for 12 hourswhile introducing nitrogen gas.

After completion of the reaction, the reaction mixture was cooled toroom temperature and the precipitated product was separated byfiltration. The product was added into 350 ml of hot toluene, and theunchanged glycol and intermediate monocarbamate were dissolved therein,followed by filtration. The residual product was dissolved in 2 litersof hot nitrobenzene and filtered. The filtrate was cooled to roomtemperature, and the precipitate was separated by filtration, washedwith toluene and dried. Some 288 g of 4,6-dimethyl-m-xylylenedicarbamate melting at 197-8C were obtained in a yield of 76 percent.

EXAMPLE 9 The same reactor as used in Example 7 was charged with 831 gmoles) of 2,5-dimethyl-p-xylylene glycol, 781 g (13 moles) of urea and40 g of di-n-butyl tin laurylmercaptide, and the reaction was carriedout at l45-150C for 11 hours while introducing nitrogen gas.

After completion of the reaction, post treatments were conducted in thesame manner as in Example 7. Some 908 g of 2,5 -dimethyl-p-xylylenedicarbamate were obtained in a yield of 72 percent. The melting point ofthe product was 219C and the nitrogen analysis value was found to be11.3 percent (calculated value 11.1 percent).

EXAMPLE The same reactor as used in Example 7 was charged with 831 g (5moles) of 4,5-dimethyl-o-xylylene glycol, 781 g (13 moles) of area and23 g of di'n-butyl tin dilaurate, and the reaction was conducted at145-l50 "C for 14 hours while introducing nitrogen gas.

After completion of the reaction post-treatment were carried out in thesame manner as in Example 7 to yield 895 g of 4,5-dimethyl-o-xylylenedicarbamate in a yield of 71 percent. The melting point of the productwas 206C and the nitrogen analysis value was found to be 10.9 percent(calculated value 11.1 percent).

EXAMPLE 11 The same reactor as used in Example 7 was charged with 691 g(5 moles) of m-xylylene glycol, 660 g (11 moles) of urea and 40 g ofdi-n-butyl tin dilaurylmercaptide, and the reaction was conducted at140-145C for 12 hours.

After completion of the reaction post treatments were carried out in thesame manner as in Example 7 to yield 830 g of iii-xylylene dicarbamatein a yield of 74 percent. The melting point of the product was 14714 8Cand the nitrogen analysis value was found to be 12.6 percent (calculatedvalue 12.5 percent).

What we claim is:

1. A process for the preparation of xylylene dicarbamates of the formulawherein R represents an alkyl group of one to for carbon atoms and n is0 or an integer of l to 4, which comprises reacting a xylylene glycol ofthe formula wherein R and n are as defined above, with urea at atemperature of to C in the presence of a catalytic amount of'a catalystselected from carboxylic acid salts of zinc or lead, stannic or stannouschlorides, and organotin compounds of the formula A SnX or A SnY whereinA is an alkyl or alkoxy group, X is halogen, thioalkoxy or hydroxyl or acarboxylic residue, Y is O orS,andmis 1,2or3.

2. A process of claim 1 wherein said urea is used in at least thestoichiornetric amount based on the xylylene glycol.

3. A process for the preparation of xylylene dicarbamates of the formulaCIiiOCONII R CH-QOCONH wherein R represents an allryl group of 1 to 4carbon atoms and n is 0 or an integer of 1 to 4, which comprisesreacting a xylylene glycol of the formula wherein R and n are as definedabove, with an ester of carbamic acid of the formula H NCOOR' wherein Rrepresents an alkyl group of one to four carbon atoms, at a temperatureof 120 to C in the presence of a catalytic amount of an aluminumalkoxide or tetralkyl titanate.

4. A process of claim 3 wherein said ester of carbam- CHQOCONHZCH2OCONH2 .ic acid is used in at least the stoichiometric amount 4111-10ONII: i oiiiocomn wherein R represents an alkyl group of one to fourcarbon atoms and n is 0 or an integer of l to 4, which comprisesreacting a xylylene glycol of the formula 7. A xylylene dicarbamate ofthe formula P -c1110}; (RA #CHZOH cnocown '2 4 3 /H l cmbcomn wherein Rand n are as defined above, with at least a stoichiometric amount ofurea based on said glycol at a where!" R represfmts alkyl group of oneto four temperature of 135 to 160C; treating the resulting atoms and n15 0 or an Integer of 1 to reaction product with an aromatic hydrocarbonof six l y y y (llcal'bamateto nine carbon atoms; treating the resultingresidue f y 'p y y dlqal'bamatewith nitrobenzene to dissolve theresulting xylylene y y y dlcarbamatedicarbamate therein; and recoveringthe xylylene dicar- 1 m'xylylene dlcal'bamatebamate from the solution.

so I

1. A process for the preparation of xylylene dicarbamates of the formulawherein R represents an alkyl group of one to for carbon atoms and n is0 or an integer of 1 to 4, which comprises reacting a xylylene glycol ofthe formula wherein R and n are as defined above, with urea at atemperature of 135* to 160*C in the presence of a catalytic amount of acatalyst selected from carboxylic acid salts of zinc or lead, stannic orstannous chlorides, and organotin compounds of the formula AmSnX(4 m) orA2SnY wherein A is an alkyl or alkoxy group, X is halogen, thioalkoxy orhydroxyl or a carboxylic residue, Y is O or S, and m is 1, 2 or
 3. 2. Aprocess of claim 1 wherein said urea is used in at least thestoichiometric amount based on the xylylene glycol.
 3. A process for thepreparation of xylylene dicarbamates of the formula wherein R representsan alkyl group of 1 to 4 carbon atoms and n is 0 or an integer of 1 to4, which comprises reacting a xylylene glycol of the formula wherein Rand n are as defined above, with an ester of carbamic acid of theformula H2NCOOR'' wherein R'' represents an alkyl group of one to fourcarbon atoms, at a temperature of 120* to 180*C in the presence of acatalytic amount of an aluminum alkoxide or tetralkyl titanate.
 4. Aprocess of claim 3 wherein said ester of carbamic acid is used in atleast the stoichiometric amount based on the xylylene glycol.
 5. Aprocess of claim 3 wherein the reaction of said xylylene glycol withsaid ester of carbamic acid is effected in the presence of a solventselected from aromatic hydrocarbons having a boiling point higher than115*C, chlorobenzene derivatives and alkoxybenzene derivatives.
 6. Aprocess for the preparation of xylylene dicarbamates of the formulawherein R represents an alkyl group of one to four carbon atoms and n is0 or an integer of 1 to 4, which comprises reacting a xylylene glycol ofthe formula wherein R and n are as defined above, with at least astoichiometric amount of urea based on said glycol at a temperature of135* to 160*C; treating the resulting reaction product with an aromatichydrocarbon of six to nine carbon atoms; treating the resulting residuewith nitrobenzene to dissolve the resulting xylylene dicarbamatetherein; and recovering the xylylene dicarbamate from the solution.
 7. Axylylene dicarbamate of the formula wherein R represents an alkyl groupof one to four carbon atoms and n is 0 or an integer of 1 to
 4. 8.4,6-Dimethyl-m-xylylene dicarbamate.
 9. 2,5-Dimethyl-p-xylylenedicarbamate.
 10. 4,5-Dimethyl-o-xylylene dicarbamate.